Have you tried browsing tutorials on Deviantart? Lots of people put up tutorials of their techniques there, and they're made by amateurs so the language is usually pretty accessible. Unfortunately, I can't think of any that are mouse-based...in principle most of the stuff ought to be mostly the same, except that your lines won't be pressure-weighted line on a tablet. But using layers, brushes, opacity, etc, should be universal.
I've always found Neondragon's tutorials to be pretty handy. This is a basic coloring one that has basic details like layer lock and opacity.
neondragonart.com/dp/photocolor1.html
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